1. Field of the Invention
The present invention relates to a process for forming a film of a high polymer and, more particularly, to a process for forming a film of a modified high polymer by the Langmuir-Blodgett process.
2. Description of the Prior Art
It was found by Langmuir and Blodgett in 1930s that fatty acids having ca. 16 to 22 carbon atoms can form a monomolecular film on the surface of water and such a film can be built up or laminated on a substrate. However, it is only recent years that investigation of their technical application was started.
The outline of investigations hitherto made has been reviewed in "Kotai Butsuri (Physics of Solids)," 17 (12), p. 45 (1982); "Thin Solid Film," 68, No. 1 (1980); ibid., 99, Nos. 1, 2 and 3 (1983); G. L. Gains, "Insoluble Monolayers to Liquid-gas Interface," Intersciene Publishers, New York (1966); etc. However, the conventional Langmuir-Blodgett films (hereinafter referred to as "LB film") of straight chain saturated carboxylic acids are not satisfactory in such points as heat resistance and mechanical strength and, so there is a problem that they can find no practical application as they are.
In order to rectify the above disadvantages, investigations have been made on polymetric films of unsaturated fatty acids, such as .omega.-tricosenic acid, .omega.-heptadecenic acid and .alpha.-octadecylacrylic acid; and unsaturated esters of fatty acids, such as vinyl stearate, octadecyl acrylate; as well as derivatives of diacetylene. Those films, however, are not sufficiently heat-resistant and have only poor electrical properties. It is also known that some hydrophilic group-containing polymers, such as polyacrylic acids, polyvinyl alcohols, polyethyl acrylates and polypeptides, also have film-forming properties. However, any sort of modified high polymer suitable for LB materials has not as yet been investigated, and there are no excellent materials for LB film worthy of the name.
On the other hand, heat-resistant films have been produced from polyimides. However, polyimide films prepared by the spin coat method or the like usually have a thickness greater than 1 .mu.m, or at best 1,000 .ANG.. It is therefore very difficult to produce a heat-resistant film having a thickness of 1,000 .ANG. or less and, at the same time, free from pin holes.